As is well known in this specific technical field, a wide range of transducers are available such as, for example, those described in the U.S. Pat. No. 5,895,998. Various types of printer heads are among the wide variety of disclosed transducers. In a piezoelectric load such as a printer head, the electronic circuit is driven by applying voltage waveforms generally formed by a series of ramps having a predetermined slew-rate. An example of such an application is disclosed in the U.S. Pat. No. 4,767,959 in the name of Nippondenso Co.
The special accuracy required for applying said voltage waveform to the load terminals, along with the high frequency of the driver signal, leads to the use of linear-mode driver circuits involving high power dissipation. Moreover, the presence of a parasitic inductance in the flat connection cable to the load, which is connected in series to the real capacitive load, requires the current demanded by the load to be filtered. The profile of this current is not rectangular and has a beveled pattern with over- and under-elongations, to produce a voltage waveform as shown in the attached FIG. 1. Therefore, with respect to an ideal case of a merely capacitive load, it is necessary to manage adequately a current slew-rate at the ramp base and a current queue at the ramp end of the capacitive load.
The features of these front end electronic circuits depend on the parasite parameters inserted by the flat cable. The structure conventionally used to apply a voltage waveform to a piezoelectric load with an inductive-resistive connection is also shown in FIG. 1 which illustrates a linear driving example. In practice, the driver circuit of FIG. 1 comprises an operational amplifier having a power output stage sufficient for load driving. The piezoelectric load is typically a non-dissipating capacitive load wherein all electric power is dissipated at the transistors incorporated in the linear driving stage. The linear driving solution is not particularly effective because of the considerable electric power dissipation.
The technical problem underlying the present invention is to provide a driver circuit, particularly for piezoelectric loads, with such functional and structural features to allow a highly efficient load driving without reducing the quality of the waveform generated at the load terminals.